Testing for internal erosion and evaluating quantitatively the observable facts

Robert P. Chapuis

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: FUNDAMENTALS - V Soil & Rock Mechanics

ABSTRACT: Simple equations and one graph summarize the criteria to predict whether or not the fine solid particles of a soil will move in its own pore space. The grain size distribution curve (GSDC) of a soil is analyzed using the recently published modal decomposition method. It is used to quantify internal erosion for a soil tested in a rigid-wall permeameter. Three lateral piezometers indicated that the material was initially homogenous. During seepage, the permeability increased in the upper portion, and decreased in the lower portion, a sign that fine particles had moved. After hydraulic stabilization, the tested specimen was divided into four parts for GSDCs. The modal decomposition showed that the specimen had three grain-size modes. The same three modes were found in the four specimen parts. For the proportions of the three modes, it was found that the upper quarter of the specimen had lost the Fine Mode, and had the highest proportion of the Coarse Mode, whereas the proportion of the Medium Mode had little variations with depth. This example demonstrates that the modal decomposition method is helpful to quantify internal erosion.

RÉSUMÉ: Des équations simples et un graphe résument les critères pour prédire si les petits grains se déplacer dans les pores du sol. La courbe granulométrique décomposition modale. On lutilise pour testé dans un perméamètre à paroi rigide. Trois piézomètres latéraux ont indiqué que le matériau était au départ homogène. perméabilité a augmenté dans la partie supérieure, et a diminué dans la partie inférieure, signe que les petits grains avaient bougé. Après stabilisation hydraulique, le spécimen testé a été divisé en quatre parties pour GSDC. La décomposition modale a montré que le spécimen avait 3 modes granulométriques. Les mêmes 3 modes ont été retrouvés dans les 4 parties. Pour les proportions des 3 modes, on a trouvé que la partie supérieure avait perdu le mode Fin et avait le plus grand pourcentage du mode Grossier, alors que le pourcentage du mode Moyen variait peu avec la profondeur. Cet exemple démontre utilité de la décomposition

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